Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $124.60   13.344%   $141.2266   $141.23   $141.25   $141.20  
  Purchase #2 $123.87   9.658%   $135.8334   $135.83   $135.85   $135.80  
  Purchase #3 $158.65   13.252%   $179.6743   $179.67   $179.65   $179.70  
  Purchase #4 $111.51   11.122%   $123.9121   $123.91   $123.90   $123.90  
  Purchase #5 $124.81   9.645%   $136.8479   $136.85   $136.85   $136.80  
  Purchase #6 $65.57   4.828%   $68.7357   $68.74   $68.75   $68.70  
  Purchase #7 $241.60   6.803%   $258.036   $258.04   $258.05   $258.00  
  7 purchase totals = $950.61       $1,044.2660   $1,044.27   $1,044.30   $1,044.10